Getting a Grip on Runways

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Over the last 15 years, more than 100 fatalities have occurred as a result of aircraft overruns directly related to "poor" runway braking action. The key to lowering this number is proper runway friction testing. While accidents like those at Chicago Midway Airport in 2005 and Broome County Airport in 1989 have led to improved technologies and testing practices, there is still room for improvement.

As the MDW accident has shown, a lack of awareness within the aviation industry and its users as to the hidden dangers of winter airport operations can lead to severe consequences. Understanding the direct relation between friction values and fluid drag or pavement contaminant, such as snow and slush, must be calculated in providing an accurate braking action report. The development of improved runway surface testing equipment along with better communications between airports, air traffic controllers, and pilots will be vital to the safety of the growing national aircraft traffic.

"Surface standards for runway pavement require two things: it has to be able to absorb and drain water at a certain rate and - if it's wet or dry - it has to support a certain amount of traction, respectively," explained John Gadzinski, a captain for Southwest Airlines.

"Once that level has been established, we know that if someone builds an airplane and say it's going to stop in a certain number of feet, it will because the airport we are testing for friction is at the same basic caliber as the runway where the airplane was certified. We know that those figures will be valid at every single runway. There are standards that runways need to meet," Gadzinski said.

Chet Collett, Alaska Airlines manager, flight standards, Alaska Airlines, would like to see the Aviation Rulemaking Committee matrix report being used. In a matrix report format the airport staff provides the runway condition rating in thirds (Touchdown-Midfield-Rollout) of the runway on a scale between one and five - one being poor and five being good.

"They would report the runway as being, for example, 3-3-3 at 75 percent compact snow. The 3-3-3 tells the pilots everything they need to know. They wouldn't need to know then what the friction reading was because the airport staff would be using that friction measurement to either downgrade the runway or validate what is actually on the runway, while reporting contaminate type and depth," he said.

Creating a Standard

Airport operators have the ultimate responsibility to provide the safest pavement surfaces using accurate and repeatable friction measurement devices, like the NAC Dynamic Friction Tester (DFT), reporting friction and contaminate type.

Runway friction testing is required when contaminate exists and needs to be reported to pilots. Using proper and calibrated devices and trained technicians who are following standardised test procedures will greatly improve airport safety during aircraft operations. Unfortunately today, many airfields are being inspected by staff who believe both a continuous friction measurement device (CFME) and a decelerometer report the same value when, in fact, they do not. The differences are clear, a decelerometer measures the "g" force or braking action (an electronic decelerometer is more accurate than mechanical); a CFME measures "mu".

Airfield operators need a full understanding of these differences and the International Friction Pavement Association has taken the first step to standardise testing procedures and to establish a certification programme for airport operators.

International Friction Pavement Association "Runway Friction Certification Program" at the Brooksville Friction Test Facility, Thomas J. Yager Research Center in Tampa Bay, Florida, USA.

In conclusion, establishing standardised testing procedures, oversight inspection of airport devices for condition and calibration, requiring airport operators to attend certification programmes, together with education, are needed to alleviate the existing problems and safety concerns surrounding runway friction.
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Author Timothy W. Neubert, MBA, A.A.E is an International Friction Pavement Association Board Member

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